This invention generally relates to devices and methods for measuring the power output of motors and the like, and more particularly to dynamometers, power absorption devices and related methods for determining the torque of a rotating shaft powered by a motor as a measure of the power of such motor. Specifically, this invention relates to an improved dynamometer and method for measuring the power output of a motor which is simple, inexpensive in construction and operation, and which considerably reduces the problem of friction heat generation inherent in prior devices and methods.
A wide variety of devices, i.e., dynamometers, and methods for measuring the power output of motors such as automobile engines, agricultural machines and other power sources, are presently available. Basically, these prior art devices fall into three broad categories: (1) mechanical braking devices and methods which depend upon frictional energy conversion, (2) hydraulic braking devices and methods which involve absorbing mechanical energy by shearing a working fluid, and, (3) electrical braking devices and methods which utilize variations in field forces or reversals in electric polarity as a means of energy conversion. Moreover, previous devices and methods have often incorporated two or more techniques from the above categories in the same device or method.
Examples of typical prior art mechanical dynamometers and methods are illustrated in U.S. Pat. Nos. 943,391; 1,718,175; 2,306,845, 3,068,689; 3,453,874 and 3,491,579. Such devices generally utilize a friction brake positioned against a rotating shaft powered by a prime mover, the torque of the shaft and thereby power of the prime mover being determined by the amount of torque applied to the brake as determined from devices secured to the brake, the rotary motion of the shaft tending to rotate the brake itself.
Examples of typical prior art hydraulic dynamometers or combinations of mechanical and hydraulic dynamometers and methods are illustrated in U.S. Pat. Nos. 2,035,576; 2,981,099; 2,993,369 and 3,757,908. In these types of dynamometers, the energy of a rotating shaft powered by a prime mover is absorbed by a fluid which in turn is converted to another form of energy which is then measured. Again, as with the mechanical devices, the control of heat generated within the dynamometer is a significant problem. While numerous cooling systems, methods and concepts have been incorporated into these various dynamometers, the problem of heat has not been satisfactorily solved for high power or high RPM applications.
One example of an electromagnetic dynamometer is illustrated in U.S. Pat. No. 2,744,409. Again, the problem of heat generation within the dynamometer is significant.
While such dynamometers and methods as disclosed in the above-noted patents have generally been adequate, the problem of heat generation is still significant. Dynamometers and similar devices and methods measure the power of a prime mover normally by rotating a shaft powered by the prime mover, and converting a portion of the kinetic energy of the rotatary components into another more measurable form. Such conversion generally occurs by partially converting the rotary motion or angular movement of the shaft to another form of motion, particularly to rotary motion of another device as is common with friction disc brake arrangements. Inherent in this conversion is a loss of energy in the form of heat resulting from friction between the rotating shaft and the element directly in contact with the shaft. This is a problem in that the contacting parts become rapidly worn unless the heat is removed. Hence, much of the above prior art is devoted to systems for removing the heat generated within the dynamometer without affecting the measuring function thereof, and many prior art devices have become cumbersome, complicated, and costly to construct and maintain due to the heat removal apparatus associated therewith.
The present invention solves this problem of heat generation not by means or methods of removing the generated heat, but rather by reducing the amount of energy converted to friction heat. This is achieved by converting or translating the rotary motion of a drive means to linear reciprocal motion of an oscillatory means with a minimum loss of evergy in the form of friction heat, and applying a resistive force to the oscillatory means in opposition to the linear motion thereof. U.S. Pat. Nos. 3,550,619 and 3,888,129 disclose arrangements whereby rotary motion is converted to linear reciprocal motion by means of a cam and cam follower. However, neither of these patents recognizes or is concerned with the application of such a principle to the measurement of the power of a motor. Moreover, these patents do not teach the application of a resistive force the translated linear motion. Thus, with very little energy loss in the form of friction heat, the present invention overcomes the heat generation problem inherent in previous dynamometers without complicating the measuring device and method with additional cooling apparatus and steps.